The present invention relates generally to crankshaft target wheels, and more particularly to binary encoded crankshaft target wheels that require only a single variable reluctance (VR) sensor but that are useful with more than one VR sensor or one or more magnetostatic sensors.
A binary coded target wheel is a disk that is engaged with a vehicle crankshaft and that is configured for inducing signals in one or more sensors positioned next to the target wheel, with the signals representing the angular position of the crankshaft to provide for fast identification of the absolute angular position of the crankshaft within, e.g., one quarter of a revolution. These position signals can be used in distributorless ignition systems that have selectively energized ignition coils that fire the spark plugs as appropriate for the angular position of the crankshaft. Moreover, the crankshaft angular position signals can be used for combustion control and diagnostic functions.
Examples of target wheels including the purpose and designs for binary encoding are set forth in, e.g., U.S. Pat. Nos. 5,570,016 and 5,731,702. Essentially, the edge of the disk-shaped wheel is varied along the periphery of the wheel in some fashion, e.g., by cutting slots in the periphery in a predetermined pattern. Usually, two sensors are used to detect the slots as they pass by the sensors, with the detected slot pattern being correlated to a crankshaft angular position.
Two sensing schemes can be used. In the first, referred to as xe2x80x9ctime-basedxe2x80x9d, each position signal pulse that is generated is actually two pulses that are spaced from each other, depending on the angular position of the wheel, in a long-short pattern or short-long pattern. Unfortunately, time-based crankshaft position systems suffer from the drawback that crankshaft rotational speed and acceleration must be accounted for, which complicates such systems and increases their cost.
Accordingly, a second sensing scheme has been developed, referred to as xe2x80x9cangle-basedxe2x80x9d, that is unaffected by crankshaft speed and acceleration. In angle-based systems, either two VR sensors or two magnetostatic sensors have been required to sense the binary pattern established by the slots. Unfortunately, using two sensors instead of one increases the cost and complexity of such systems. Moreover, in angle-based systems VR system wheels are not appropriately configured for magnetostatic sensor systems, and vice-versa, requiring duplicative design and production costs. The present invention has recognized the above-noted problems and has provided the below solutions to one or more of the prior art drawbacks.
A target wheel for ascertaining the angular position of a crankshaft includes a wheel body that has a periphery defining a nominal radial surface. The nominal radial surface is characterized by a nominal wheel radius. Moreover, the periphery of the wheel is formed with plural slot radial surfaces, each being characterized by a slot radius that is less than the nominal wheel radius. Further, the periphery of the wheel is formed with plural tooth radial surfaces. Each tooth radial surface is characterized by a tooth radius that is greater than the nominal wheel radius.
Preferably, each slot defines a slot angular width and each tooth defines a tooth angular width, and the slot angular width is larger than the tooth angular width. Additionally, each slot defines a slot radial depth relative to the nominal wheel radius and each tooth defines a tooth radial height relative to the nominal radius, and the slot radial depth is larger than the tooth radial height. In other words, to achieve magnetic symmetry between slots and teeth the slots are larger than the teeth. The wheel can be used in combination with at least one sensor in the group of sensors consisting of VR sensors, magnetostatic sensors, preferably such as Indium-Antimony (InSb) magnetoresistor (MR) sensors, and Hall effect sensors.
In another aspect, an angular-based crankshaft position sensing system includes a target wheel having a periphery that defines a binary pattern, and one and only one VR sensor is juxtaposed with the target wheel and is responsive to the binary pattern to generate a signal representative of the position of the target wheel.
In still another aspect, a crankshaft target wheel includes a wheel body having a nominal periphery. Plural teeth rise from the nominal periphery and plural slots fall from the nominal periphery.
The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: